Electric heating device



April 1951 J. M. CUMMiNG ET AL 5 9 ELECTRIC HEATING DEVICE Filed Sept. 16, 1.946

22 w 19 if 12 fiame Z22. Gammzng" Wayne d5 @Jgeg Patented Apr. 10, 1951 ELECTRIC HEATING DEVICE James M. Cumming and Wayne S. Aspey, Turtle Creek, Pa., assignors, bymesne assignments, to

' the United States of America as represented by the United States Atomic Energy Commission Application September 16, 194 Serial No. 697,206

The present invention relates to electric heating devices and more particularly to the means of fastening the grounded end of ,a metalencased, oxide-filled heater element to' the metal casing to provide a terminal end.

H In certain types of electric heating devices, the use of a heating wire or element enclosed or 'encased in a metal sheath has become quite common. Such heating units usually employ a granular refractory material such as magnesium-oxide as an insulating filling within the sheath to prevent electrical contact between the metal sheath and the electric heating wire. Also, it is the usual practice to electrically connect one end of the heating wire to the metal sheath thus providing a grounded end so that an electrical circuit may be established through the heater wire by connecting the terminals of a power source to the unconnected end of the heater wire and to the grounded metal sheath. The characteristics of the magnesium-oxide filler material are such that quantities of gases are evolved when such material is subjected to heat. Considerable trouble has therefore been encountered when soldering, welding or otherwise electrically and mechanically connecting the grounded end of the heater wire to the metal sheath because of the necessary application of heat to the metal sheath which is transmitted to the magnesium-oxide filler. This is particular objectionable when the grounded end of the heater unit comprising the end of the sheath to which the heater wire is joined, is required to have a vacuum-tight joint; the gassin of the magnesium-oxide filler upon the application of heat having the tendency to cause porosity in the welded joint.

It is therefore a principal object of this invention to provide a means of electrically and mechanically joining the grounded end of a heater wire encased in a refractory-oxide filled metal sheath to the metal sheath in such manner as to provide a vacuum-tight joint, there being provision for the escape of gases evolved from the oxide filler before the final vacuum-tight joint is made and provision for the entrapment of the heat generated in the final joining operation to prevent the heat from further affecting the oxide to cause the generation of gases.

Further objects and advantages of this invention will be apparent by reference to the following specification and drawing in which:

Fig. 1 is a side elevation partly in section of the grounded heater end to show the joint of this invention; and

3 Claims. (01. 201-63) Fig. 2 is a perspective elevation of the spacer element used in the invention.

In Fig. 1 of the drawings, a portion of a metal encased heating unit is shown to be comprised of an outer metallic sheath l0 filled with a granular refractory insulating material such as magne sium-oxide H and enclosing an electric heating wire I2. The electric heating wire I2 is fastened at l3 to a terminal member l4 which in the case of the grounded end of the heater unita's shown is to be electrically and mechanically connected to the metal sheath 10. A washer disk l5 formed of any suitable material and having a central i aperture I6 slightly larger in diameter than the terminal His inserted as shown to retain the magnesium-oxide filler II in place. A metallic spacer member l1, shown in perspective in Fig.2, is likewise provided with a central aperture ll! of slightly larger diameter than the terminal I4 and is inserted within the endof the sheath 10 as shown in'Fig; 1; Itwill benoted that the depending legs IQ of the spacer l'l are'so arranged to abut the washer disk l5 and to provide a dead air space 20 for the entrapment'of vapors-generated during the final joining operation.

With the spacer [9 in place as shown in Fig. 1, heat is applied to the ends of the metal sheath and spacer to produce the fused weld 2|. During this heating and welding operation, any gases evolved from the magnesium-oxide filler II are permitted to escape through the spaces between the terminal 14 and the slightly larger apertures l6 and I8. Thereafter, the entire end of the heater unit between the cupped end 22 of the spacer I1 and the end of the terminal [4 is filled with weld or solder metal 23 as shown. During this final joining operation, the applied heat is entrapped within the dead air space 20 and thus prevented from reaching the magnesium-oxide filler material II in such magnitude as to cause more gases to be evolved which would tend to create pores in the weld material 23 forming the final vacuum-tight joint. Thus, in such manner, a vacuum-tight joint for the grounded end of a metal encased and oxide filled heater unit is obtained.

Considering the foregoing description, it will be noted that when applyin the relatively large amount of heat to effect the welding of the sheath to the spacer I! at M, the gas evolved from the refractory-oxide filler is permitted to escape through the apertures l6 and 18. However, to effect the weld at 23, the heatis not applied directly to the sheath I0 but is transmitted u thereto only through the spacer element [1 and 5 Di; ai

' to its legs I9. This feature when combined with the dead air space 20 prevents the application of any great amount of heat to the refractoryoxide I I so that no gases are evolved to deleteriously affect the weld 23 and produce pores therethrough,

We claim V v v 1. An electric heatin device comprising a metallic sheath containing a granular refractory filler material and enclosing an electric heater wire, a metallic spacer member insertedwithin and welded to one of the terminal, endscf said,

sheath, said spacer member having. a central 1 aperture to receive the terminal end 19f said elec';

bein i ligh ly tric heatin wire, said apertugreater diameter than the diameter of the terminal end of said heating wire, a diskwas-her:

having a central aperture slightly largei tl'i alls the diameter of the terminal end of said heating Wire s i (Washer-bei eeositioned. reund. h terminal end of said heating wire. and within said sheath between the filler material. and csaid a-per,, s id: a er being s aped, t ovide. a

air sp e betweenv'said Washer. andfthe .end: of

tlr that} is devoid of said granular retel yemater a r h a r i i s id heating wirebeing welded to said spacer in thefire'gion of the spacer apertureto provide a vacuum-tight joint between the spacer and said terminal end, here hsaidiapertures. V p 2, An elec tr-ic heating :device .comprising a n neles ne a i ee r eh er a "c; spa er; membe rinserted within and tonne,- o the-t rmin le ds of d She th W er member having a central; aperture ve the terminal end ofsaid electric heate, said aperture'being of slightly greater ter than the diameter of the terminal end eat n W re d a r. e n ha e impr ve/1amia ris e ewq y ii-sai r: m

e lved i on; Said 'filllera eria i urnewthe beginning, 0 w lding eper ien e I hee wc nta mnee-m en iumeo i i jtric heatingrwire, said aperture bein of slightly greater diameter than the diameter of the terminal endof said-heating Wire, a disk washer having a central aperture slightly larger than the diameter of the terminal end of said heatth rminal en e esaidh ine' W a Withi sa sheath between thefiller materialand said spaceggsaidspacer being shaped toprovide an air spacebetween said washer and the endof said sheath that is devoid of said 'filler' material, the terminal end of'- said heating wire; being weldedto" said spacer in, the region ofthespa'cer 'aperturatoprovide a vacuum-tight joint-between the spacerand: saidterminal-- end; -the gases evolved from said; filler material duringthe beginning of the welding operation escaping throllghsaid apertures-1 I J 'M: CUMMIN W Y Si: AS Y-j.

REFERENCES CITED The following references are of record, inthe .f e 9 pa ent;

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